1. Field of the Invention
The present invention relates to a linear motion rolling guide unit, in which a slider having a casing slides along a track rail with a number of rolling elements interposed therebetween.
2. Description of the Prior Art
In a conventional linear motion rolling guide unit, a slider that slides on a track rail consists of a casing, end caps fixed to both ends of the casing, end seals attached to the end caps, and an under seal provided to the underside of the slider. A linear motion rolling guide unit as shown in FIG. 10 is known. The unit generally consists of a track rail 1 having raceway grooves 27 formed on longitudinally extending side walls 26 thereof, and a slider 2 slidably mounted astride the track rail 1. The slider 2 includes a casing 3, which is slidable relative to the track rail 1 and has raceway grooves 29 formed at positions facing the raceway grooves 27 on the track rail 1, a number of rolling elements 5 roll-running between the opposing raceway grooves 27 and 29 relatively movable therebetween, and end caps 12 attached to the longitudinal ends (in a sliding direction) of the casing 3, the longitudinal direction being the sliding direction of the casing 3. The end cap 12 has at its end surface an end seal 28 that provides the sealing between the track rail 1 and the slider 2. The casing 3 is provided with under seals 30 for sealing the underside of the casing 3 and the end caps 12 and also the longitudinally extending side walls 26 of the track rail. The slider 2 is mounted astride the track rail 1 and freely slidable relative to it through a number of rolling elements 5 formed as balls circulating along the raceway grooves 27 in the track rail 1. The rolling elements 5 are circulating through a raceway 32 formed between the raceway grooves 27 and 29, a direction changing passage (not shown) formed in the end cap 12 and a return passage 31 formed in the casing 3.
What is shown in FIG. 9 is an example structure of the conventional linear motion rolling guide unit showing how the under seal 30 is mounted to the casing 3. Components of the linear motion rolling guide unit of FIG. 9 that are identical to the corresponding ones shown in FIG. 10 are assigned like reference numerals. In FIG. 9, the slider 2 has the under seal 30--which is a plate body formed at one side with a lip portion 20 in sealing contact with the longitudinally extending side walls 26 of the track rail 1--arranged at the underside of the casing 3 and the end caps 12 mounted to the longitudinal ends of the casing, the longitudinal direction being the sliding direction of the casing 3. The under seal 30 is fixed by inserting screws through through-holes formed in the under seal 30 and fastening the screws into threaded holes in the casing 3.
Because the under seal 30 is mounted to the casing 3 by a fixing means 33 such as rivets and screws, its mounting and dismounting is troublesome. Although the under seal 30 has the advantage of being simple in shape and therefore easily manufactured, there are drawbacks that positioning errors easily occur with respect to the casing 3 and the track rail 1, in which raceway grooves 27, 29 are formed, and that because the under seal 30 is thin, it is easily deformed by external force and heat. This in turn gives rise to a problem that when the slider 2 slides on the track rail 1, the under seal 30 may undergo deformations such as elongation due to temperature changes and swell caused by lubricating oil, resulting in buckling in the longitudinal direction and degradation in sealing performance.
In the conventional linear motion rolling guide unit, to accommodate a retainer plate for fixing the track rail to a bed or to prevent foreign matters such as dust or cutting chips from entering the raceway grooves from the under seal, a gap H1 must be provided between the lower end of the slider 2 and the lower end of the track rail, i.e. the upper surface of the bed 36, as shown in FIG. 9. However, because the lower ends of the end cap and of the casing are formed with the rolling element direction changing path and the rolling element circulation path, respectively, the lower ends of the end caps and casing could not be cut short.
Further, when the linear motion rolling guide unit has the structure shown in FIG. 9, in which the under seal 30 is fixed to the casing 3 by inserting screws 33 through through-holes in the under seal 30 and into threaded holes in the casing 3, the threaded holes must be formed in the casing 3, increasing the manufacturing cost. In the conventional linear motion rolling guide unit, the under seal is mounted to the undersides of the casing and of the end caps attached to the longitudinal ends of the casing, so that the under seal and the screws are located below the lower ends of the casing and the end caps, making it impossible to secure the large enough gap H1 between the lower end of the slider and the lower end of the track rail, i.e. the upper surface of the bed.
Japanese Utility Model Laid-Open No. 98321/1991 discloses a linear motion rolling guide unit, in which the axial end portions of the under seal are folded back inwardly to be formed into a U-shape; in which the folded surfaces are provided with inwardly projecting engagement portions; and in which the outer end of each end cap is formed with a recess that receives the engagement portion of the under seal. This construction has a drawback that the under seal, not made of a core bar lower surface member, may get deformed in the longitudinal direction.
Japanese Patent Laid-Open No. 164128/1993 discloses another linear motion rolling guide unit, in which the under seal consisting of a core bar lower surface member and an elastic member having a lip portion and secured to the core bar lower surface member is placed at the undersides of the casing and of the end caps attached to the longitudinal ends of the casing and is secured to the end seals placed in contact with the end caps. Although the under seal of this linear motion rolling guide unit uses a core bar lower surface member, there is a limit to the thickness of the under seal because it is attached to the underside of the casing, making it difficult to secure a large enough gap between the lower end of the slider and the lower end of the track rail.
In the linear motion rolling guide unit disclosed in Japanese Utility Model Application No. 91496/1992 previously filed by this inventor, the under seal--which has locking bands that extend externally widthwise at the longitudinal end portions of the core bar member fixedly attached with an elastic member, and locking claws that are formed by bending the free ends of the locking bands toward the end caps--is fitted in a recessed portion formed in the lower part of the end caps on the track rail side.